The present invention relates to wireless communication systems, and more particularly to reducing the latency experienced by users whilst scanning through available content, such as television programs, in a DVB-H based wireless communication system.
A wireless communication system implementing Digital Video Broadcasting for Handheld (DVB-H) typically offers a variety of programming (content) for presentation to a user of a mobile receiving device. The content typically includes video content to be displayed on the mobile receiver, but in general, the content carried in any particular channel is not limited to content or media having a video portion. The user of a mobile device or DVB-H receiver may operate the device in a manner that is most analogous to the operation of a television or radio. The user may selectively tune or otherwise control the mobile device to receive a particular channel from a channel line-up or catalog. Briefly scanning channels for desired content is typically referred to as channel “surfing.” In the following, the term channel is understood to refer to a logical channel that may be selected by the user, and the physical channel on which the signal is received is referred to alternatively as the frequency.
Channel switching latency arises because the DVB-H standard recommends time-slicing to reduce the power consumed by receivers while receiving a video stream. A time slice burst could contain as much as 191 KB of application data belonging to one or more media streams being viewed by an end user. Further, since the peak data rate is as high as approximately 20 Mbps and the average data rate is as low as approximately 384 Kbps, time slice bursts of a single service could be spread apart in time by as much as 5 seconds. Typically, the receiver is aware of the time of arrival of the next time slice burst of interest and turns its radio front end off at other times in order to conserve power.
When a user requests (via the user terminal or interface) to view a new channel, the mobile TV application maps the request to an IP stream carried within the DVB-H time slices by looking up a menu of available programs in an Electronic Service Guide (ESG). This IP stream is in turn mapped in the DVB-H receiver to a program, comprising MPEG-2 transport stream (TS) packets bearing a unique packet identifier (PID). These TS packets carry their payload datagrams in the MPE (multi-protocol encapsulation) syntax.
The receiver must open up or otherwise energize its radio front end until TS packets bearing the selected PID are received, which may be for up to 5 seconds in the worst case. Further, a complete burst may need to be received before packet errors are corrected via Reed-Solomon decoding, and the user may view the video from the selected channel.
Since a burst may be as large as 256 KB, the memory available in the receiver device limits the number of streams that may be received and transferred to an application for storage in anticipation of a channel-change request by the user. It is typically undesirable to monitor and store all available channels, because of the amount of memory needed to support all channels. Additionally, the receiver would suffer from reduced battery life, because the receiver would need to monitor all time slices and thus could not offer any power savings available through time slicing.
However, reducing the channel change latency is advantageous for providing a favorable user experience. Users typically do not experience latencies on the order of 5 seconds when changing channels on other communications systems, such as television or radio broadcast systems. It is desirable to reduce channel changing latency in a DVB-H wireless communication systems in order to provide a comparable, if not more favorable, user experience.